In x-ray imaging, an examination object is trans-irradiated in at least one direction by x-radiation, and the intensity of the x-radiation impinging on an x-ray detector opposite the x-ray source is measured. The measured intensity I is a function of the absorption properties of the trans-irradiated material, and of the path of the x-ray through the trans-irradiated object. In accordance with the law of absorption, the measured intensity I depends in this case exponentially on the irradiated intensity I0, in which case it holds that I/I0=e−μ/(x)dx. As a rule, in x-ray imaging the signal processing is performed by digitization and logarithmation of the measured signals such that the attenuation value distribution μ(y,z) or μ(x,y,z) of the examination object can be obtained. Logarithmated signals are also used in computer aided tomography (CT).
A fundamental problem in x-ray imaging is represented by scattered radiation, which leads to a reduction in the image contrast, in particular to a undesired brightness fog over the entire image. In the case of imaging x-ray devices having one x-ray source, use is made upstream of the detector of so-called scattered beam collimators that uncover upstream of each detector element only the direct radiation direction between the detector element and focus of the x-ray source, and largely shade all other directions. It is possible in this way for a large fraction of the scattered radiation that is produced by transverse scattering of the x-rays at the volume elements of the examination object not to reach as far as the detector elements.
Even in the case of x-ray imaging devices having a number of x-ray sources, so called two- or multifocussed/detector systems, use is made of such scattered beam collimators upstream of the detector elements. In any case, in these systems scattered beam collimators cannot reduce the scattered radiation that is produced by beams from an x-ray source arranged at an angular offset and which has the same spatial orientation as the direct x-ray beam from the x-ray source opposite the detector. This undesired scattered radiation leads to corruption of the measured data and thus to image artifacts.
DE 102 32 429 B3 discloses a method for scattered radiation corruption in an x-ray imaging device having two x-ray sources and two x-ray detectors. In the method of this publication, the two x-ray sources arranged at an angular offset from one another are operated at least temporarily in an alternating fashion in order to measure directly in the image system composed of x-ray source and x-ray detector, which image system in each case is not switched on, the scattered radiation actually occurring that originates from the x-ray source in operation in the second image system.
Measured data of the respective image systems can then be corrected on the basis of the respectively measured scattered radiation distribution. However, carrying out this method requires the x-ray sources to be operated at least partially in alternating fashion, and so at these times image information from the measurement pass is lacking, at least in the detector of the image system that is not being operated. These gaps in the data acquisition are disturbing, particularly in the case of CT cardio pictures, which require a high temporal resolution.